1. Field of the Invention
The present invention relates to a network in which a plurality of nodes are interconnected in a ring-like manner and, more specifically, to a method and a system of collecting information indicating operation states of the respective nodes.
2. Description of the Prior Art
With the increase of the scale of ring networks in recent years, countermeasures against network faults are increasingly becoming an important theme. The network faults are classified into node faults and transmission line faults. While the transmission line faults are now very rare by virtue of the introduction of optical transmission lines, the node faults occupy a large proportion of the network faults. Particularly in a large-scale ring network having a large number of nodes, since the probability of occurrences of node faults is accordingly high, it is important to quickly identify a node of fault occurrence and effect a proper measure.
An example of a fault detecting method in a ring network is disclosed in Japanese Patent Application Laid-open No. Sho 63-246946, and will be explained below. Referring to FIG. 1, in a ring system in which a supervisory node SN and ordinary nodes N.sub.1 -N.sub.5 are interconnected to form a loop, a communication between nodes is performed by circulating a data frame 10 in a direction indicated by arrows. The data frame 10 includes a destination address DA, a source address SA, a use indication B/I indicating whether the data frame 10 is in use or not, and a supervisory indication bit M.
When a certain node attempts to use a data frame 10 for an internode communication, it sends the data frame 10 to a ring transmission line after setting its use indication B/I and resetting its supervisory indication M. Receiving the data frame 10, which is in use, the supervisory node SN sends it to the ring transmission line after setting the supervisory indication M. When the data frame 10 is received by the destination node and then sent to the ring transmission line, at least the supervisory indication M is reset at that time. If the data frame 10 is not received by any node, it is again received by the supervisory node SN with both of its use indication B/I and supervisory indication M in a set state. Therefore, the supervisory node SN can identify a node of fault occurrence by analyzing the destination address and the source address of the data frame 10 whose use indication B/I and supervisory indication M are both in a set state.
However, in the above ring network system, since a data frame is circulated through the ring network only in a single direction to obtain fault information, a large-scale network in which a large number of nodes are interconnected requires long time to collect fault information. Further, since a data frame circulates only in a single direction, when a fault of disabling transmission occurs somewhere in the ring network, it is impossible to collect fault information of all the nodes existing downstream of the location of fault occurrence, which is a serious problem in dealing with network faults.